The invention is generally related to recesses in explosive carrier housings (such as perforating gun carrier housings) that provide for improved explosive performance (such as improved performance perforating shaped charges).
After a well has been drilled and casing has been cemented in the well, perforations are created to allow communication of fluids between reservoirs in the formation and the wellbore. Shaped charge perforating is commonly used, in which shaped charges are mounted in perforating guns that are conveyed into the well on a slickline, wireline, tubing, or another type of carrier. The perforating guns are then fired to create openings in the casing and to extend perforations into the formation.
Various types of perforating guns exist. A first type is a strip gun that includes a strip carrier on which capsule shaped charges may be mounted. The capsule shaped charges are contained in sealed capsules to protect the shaped charges from the well environment. Another type of gun is a sealed hollow carrier gun, which includes a hollow carrier in which non-capsule shaped charges may be mounted. The shaped charges may be mounted on a loading tube or a strip inside the hollow carrier. Thinned areas (referred to as recesses) may be formed in the wall of the hollow carrier housing to allow easier penetration by perforating jets from fired shaped charges. Another type of gun is a sealed hollow carrier shot-by-shot gun, which includes a plurality of hollow carrier gun segments in each of which one non-capsule shaped charge may be mounted.
Another type of gun is a puncher gun, designed to perforate the interior tubing, casing, drillpipe or similar wellbore lining while leaving the exterior tubing, casing, drillpipe, drill collar or similar wellbore lining intact. Another type of gun is a cutter designed to perforate the tubing, casing, drillpipe, drill collar or similar wellbore lining in a pattern which will allow removal of same without damage to the formation or other wellbore structures.
Referring to FIGS. 1A-1C, an example of a conventional perforating gun 10 including a hollow carrier 12 is illustrated. The hollow carrier 12 contains plural shaped charges 20 that are attached to a strip 22. Alternatively, the shaped charges 20 may be attached to a loading tube inside the hollow carrier 12. In the illustrated arrangement, the shaped charges 20 are arranged in a phased pattern. Non-phased arrangements may also be provided.
The hollow carrier 12 has a housing that includes recesses 14 that have generally circular recesses, as illustrated in FIG. 1A. The recesses 14 are designed to line up with corresponding shaped charges 20 so that the perforating jet exits through the recess to provide a low resistance path for the perforating jet. This enhances performance of the jet to create openings in the surrounding casing as well as to extend perforations into the formation behind the casing.
As shown in the cross-sectional view of FIG. 1B and the longitudinal sectional view of FIG. 1C, each recess 14 includes a bottom surface 18 and a side surface 16. A web 19 (which is a thinned region of the carrier housing 12) is formed below the recess 14. The side surface 16 and the bottom surface 18 are generally perpendicular to each other. The bottom surface 18 and side surface 16 define a generally cylindrical geometry in the recess 14. As will be described below, the generally perpendicular side surface 16 of a typical recess 14 causes reflection of compression waves that interfere with the perforating jet (from a fired shaped charge) as it extends through the recess 14. For big hole charges, this reduces the opening in the casing created by the perforating jet. For deep penetrating charges, the depth of penetration may be reduced.
Referring to FIGS. 2A-2B, a generally conical shaped charge 20 includes an outer case 32 that acts as a containment vessel designed to hold the detonation force of the detonating explosive long enough for a perforating jet to form. The generally conical shaped charge 20 is a deep penetrator charge that provides relatively deep penetration. Another type of shaped charge includes substantially non-conical shaped charges (such as pseudo-hemispherical, parabolic, or tulip-shaped charges). The substantially non-conical shaped charges are big hole charges that are designed to create large entrance holes in casing. Another type of shaped charge is a puncher charge which is a specialized version of a big hole charge designed to create large hole with a specific, short range of penetration.
The conical shaped charge 20 illustrated in FIG. 2A includes a main explosive 36 that is contained inside the outer case 32 and is sandwiched between the inner wall of the outer case 32 and the outer surface of a liner 40 that has generally a conical shape. A primer 34 provides the detonating link between a detonating cord (not shown) and the main explosive 36. The primer 34 is initiated by the detonating cord, which in turn initiates detonation of the main explosive 36 to create a detonation wave that sweeps through the shaped charge 20. As shown in FIG. 2B, upon detonation, the liner 40 (original liner 40 represented with dashed lines) collapses under the detonation force of the main explosive 36. Material from the collapsed liner 40 flows along streams (such as those indicated as 49) to form a perforating jet 46 along a J axis.
The tip of the perforating jet travels at speeds of approximately 25,000 feet per second and produces impact pressures in the millions of pounds per square inch. The tip portion is the first to penetrate the web 19 below the recess 14 in the housing 12 of the gun carrier. The perforating jet tip then penetrates the wellbore fluid immediately in front of the web and inside the geometry of the recess 14. At the velocity and impact pressures generated by the jet tip, the wellbore fluid is compressed out and away from the tip of the jet. However, due to confinement of the wellbore fluid by the substantially perpendicular side surface 16 of the recess 14, the expansion, compression, and movement of the wellbore fluid is limited and the wellbore fluid may quickly be reflected back upon the jet at a later portion of the jet (behind the tip).
As the perforating jet passes through the recess 14 (FIGS. 1B and 1C), a compression wave front is created by the perforating jet in the fluid that is located in the recess. When the compression wave impacts the side surface 16, a large portion of the compression wave is reflected back towards the perforating jet, which carries the wellbore fluid back to the jet. The reflected wellbore fluid interferes with the perforating jet. The effect is more pronounced in a relatively deep recess with a perpendicular side surface (such as side surface 16), or if the clearance between the gun carrier and the casing is limited (that is, the gun carrier is close to the casing). When the clearance between the gun carrier and the casing is limited, interactions between the reflected compression wave off the inside surface of the wellbore casing and the reflected compression wave off the side surface 16 of the recess 14 also combine to impede the free passage of the shaped charge jet through the wellbore fluid. The resultant interference with the perforating jet may reduce the depth of penetration (for deep penetrating charges) or the size of the casing entrance hole (for big hole charges).
In addition to the desire to improve performance of the perforating jet, the recess formed in a gun carrier housing should also account for other factors. As shown in FIGS. 1B and 1C, the recess 14 is formed below the outer surface of the carrier housing 12. As the shaped charge perforating jet passes through the web 19 of the carrier housing 12, an exit burr may be created that protrudes towards the outside of the carrier housing. However, by having recesses (and webs below the recesses) for the jets to pass through, the exit burr is kept below the external surface of the wall of the carrier housing. In this way, the sharp and hard exit burr is kept from touching and scratching the inside surface of the wellbore casing or other components in the wellbore to prevent damage to such components as the gun is being retrieved to the surface.
In forming the recesses, the recesses are made relatively deep to reduce the resistance path for a perforating jet, but not so deep that the carrier housing is unable to support the external wellbore pressures experienced by the gun carrier. The size of the recesses are also optimized to ensure that jets pass through the recesses and not through the carrier housing around the recesses. However, the sizes of the recesses are limited to enhance the structural integrity of the carrier housing in withstanding external wellbore pressures and internal forces created by detonation of the shaped charges.
The generally cylindrical geometries of some conventional recesses provide for relatively reliable carrier housing integrity. However, as explained above, such a geometry causes interference that may adversely affect the performance of the perforating jets. Other types of recess geometries are also available. For example, some may have generally elliptical shapes. However, such recess geometries may come at the expense of carrier housing integrity, since the recesses may take up too much surface area of the carrier housing, or remove too much carrier housing material.
A need thus continues to exist for improved recesses in gun or other explosive carrier housings that improve performance of shaped charges or other explosives without sacrificing integrity of the carrier housing.
In general, according to one embodiment, a carrier for containing explosives includes a housing having a plurality of recesses, each recess having a periphery and a side surface extending around the periphery and shaped to control the reflection of compression waves generated in response to an explosive jet created due to detonation of an explosive.
Other embodiments and features will become apparent from the following description, from the drawings, and from the claims.